Today's buildings are air-tight to help maintain heat and conserve energy, although ventilation is still necessary for healthy air flow. Yet most ventilation still works in the same way as opening a window – losing warmth.

The latest systems overcome this by extracting heat from the stale/outgoing air and using it to warm the fresh/incoming air. This is energy-efficient because, by retaining the air's warmth, less demand is made of any heating system.

The Lossnay ventilation system from Mitsubishi has perfected this. Installed in an attic or ceiling void, its heat-exchange core recovers up to 70% of the warmth from the outgoing air, transferring it to the incoming air which is then circulated via ducting to ceiling vents. When reversed, the system provides cooler but fresh internal air, whilst stale warm air is drawn away – making for a pleasant ambience in bedrooms on summer nights, and assisting the energy-efficiency of air-conditioning systems. The Lossnay system also removes odours and humidity, therefore of additional benefit in kitchens and bathrooms.